1. Field
This application relates to wireless communications and, more particularly, to a method and apparatus for extending a mobile unit data path between access points in a wireless network.
2. Description of the Related Art
Wireless networks generally include one or more access points located in an area to provide wireless services to mobile units with the area. Generally, a particular access point will be selected to provide wireless service to a given mobile unit. The selection may be based on quality of signal, load at the access point, and a number of other factors. Once selected, the mobile unit will communicate through the access point to receive wireless communication services on the wireless network. Although there are many different wireless protocols, the focus of this application will be on a protocol defined in the IEEE 802.11 standard.
As a mobile unit moves within a wireless network, it may move away from the access point that is providing it with service and need to find a new access point with which it may connect. The process of changing associations from one access point to another access point is commonly referred to as a handover. A mobile unit may need to perform a handover in other situations as well, for example where the access points are mobile, where an access point experiences failure, or in other situations where network conditions make it more desirable for a mobile unit to interface with a different access point.
When security is implemented on a wireless network, such as when 802.11i is implemented, the handover process may be relatively computationally intensive and require the mobile unit and access point to exchange many messages. Examples of the types of messages that may be exchanged include authentication request and response messages, reassociation request and response messages, security handshake messages such as the four-way 802.11i handshake or messages associated with the full authentication process specified in 802.1X. Additionally, the mobile unit and access point may exchange quality of service information such as the information specified in 802.11e (TSPEC), and optionally other messages. The processing associated with generating and responding to these messages may take a fair amount of time, which delays the handover between access points.
In addition to the messaging between the mobile unit and the access point, additional exchanges also may be required in connection with the handover. For example, the access point may be required to exchange messages with a back-end Authentication Server (AS), policy server (PS) in 802.11e, or other types of servers. The distance between the access point and these servers, the speed of the back-end network, the number of exchanges that must take place, and the congestion at the servers, all may contribute to delaying handovers between access points. Where the mobile unit is actively receiving or transmitting data, such as in connection with Voice over Internet Protocol (VoIP) and audio or video streaming, a relatively long handover-induced delay may be unacceptable. Particularly in situations where a given mobile unit may need to handover between access points relatively frequently, the delays associated with performing handovers may become unacceptable.
One way to attempt to accelerate the handover process is to cause some information associated with the mobile unit to be stored at neighboring access points other than the access point that is currently handling communications for that mobile unit. If a handover to a neighboring access point is then required, the theory is that the access point will have already completed part of the handover process to thereby enable the handover to occur more quickly. While this may work in particular situations, it requires every mobile unit to be known on multiple access points. This requires access points that are not responsible for a given mobile unit to expend processor resources to begin the handover process, and to use up valuable memory space to store information about a mobile unit that may never become active on that access point.